I am editing a project that contains both 16:9 anamorphic and conventional 4:3 video material. The anamorphic material is pre-squeezed (it was shot with an anamorphic lens). I need to find a way to create the final project where the 4:3 material is windowboxed (black bars on the sides) when played back on a widescreen TV in anamorphic mode.

I actually DID this successfully in a test 2 weeks ago, but now I cannot remember how I did it! This is driving me crazy!